Cold Pack Chemistry: Exploring Endothermic and Exothermic Reactions

Overview

How do "instant" cold packs get cold when they are stored at room temperature, unlike a regular ice pack which must be stored in the freezer? In this lesson plan, students will explore several endothermic and exothermic reactions, and use their observations to choose the chemical reaction that best fits the design constraints for their own chemical cold pack.

NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:

• MS-PS1-6. Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes.
• MS-ETS1-1. Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

This lesson focuses on these aspects of NGSS Three Dimensional Learning:

Science & Engineering Practices	Disciplinary Core Ideas	Crosscutting Concepts
Analyzing and Interpreting Data. Analyze data to define an optimal operational range for a proposed object, tool, process, or system that best meets criteria for success.	PS1.A: Structure and Properties of Matter. Some chemical reactions release energy, others store energy. ETS1.A: Defining and Delimiting Engineering Problems. The more precisely a design task's criteria and constraints can be defined, the more likely it is that the designed solution will be successful. Specification of constraints includes consideration of scientific principles and other relevant knowledge that are likely to limit possible solutions.	Energy and Matter. The transfer of energy can be tracked as energy flows through a designed or natural system.

Materials

For the entire class:

• Optional: at least one instant cold pack for a demonstration
• Access to a sink
• Paper towels
• Well-ventilated area or fume hood

Each group will need:

• 50 mL (or larger*) beaker
• Cup or other container for pouring water/vinegar
• Spatula or spoon for chemicals
• Access to a scale
• Partial immersion thermometer
• Optional: stirring rod
• Disposable gloves
• Chemical safety goggles
• Ammonium chloride
• Magnesium sulfate
• Sodium bicarbonate (baking soda)
• Tap water
• Vinegar

* A 50 mL beaker will allow you to immerse the thermometer bulb in about 20 mL of water. If you use larger beakers, you will need to make sure you use enough water to immerse the thermometer bulb, and increase the amounts of the other reactants proportionally so you maintain the same concentrations.